This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application FUSING DEVICE OF ELECTROPHOTOGRAPHIC IMAGE FORMING APPARATUS filed with the Korean Intellectual Property Office on Aug. 25, 2001 and there duly assigned Serial No. 51583/2001, which was subsequently published on the Mar. 4, 2003 as Publication No. 2003-17940 by the Korean Intellectual Property Office.
1. Technical Field
The present invention relates to a fusing device for an electrophotographic image forming apparatus and, more particularly, to a fusing device using a heat pipe to decrease power consumption and allow flash heating in an electrophotographic image forming apparatus.
2. Related Art
Electrophotographic image forming apparatuses include a fusing device for heating a sheet, to which a toner image is transferred, to fuse and fix the toner image in a powder state to the sheet. The fusing device includes a fusing roller for fusing and fixing a toner to a sheet and a pressing roller for pressing the sheet against the fusing roller.
A fusing roller unit includes a cylindrical fusing roller and a halogen lamp installed inside the fusing roller and along its axis. A Teflon coating layer is formed on the surface of the fusing roller. The halogen lamp generates heat within the fusing roller, and the fusing roller is heated by the radiant heat emitted from the halogen lamp.
A pressing roller is disposed below the fusing roller unit and in contact with the fusing roller such that a sheet passes therebetween. The pressing roller is elastically supported by a spring so that it makes the sheet closely contact the fusing roller with a predetermined pressure when the sheet passes between the fusing roller and the pressing roller. A toner image formed on the sheet in a powder state is fused and fixed to the sheet by predetermined pressure and heat when the sheet passes between the fusing roller and the pressing roller.
A thermistor for measuring the surface temperature of the fusing roller and a thermostat for cutting off the supply of power when the surface temperature of the fusing roller exceeds a predetermined set value are provided at one side of the fusing roller. The thermistor measures the surface temperature of the fusing roller and transmits an electric signal corresponding to the measured temperature to a controller of a printer. The controller controls the quantity of electricity supplied to the halogen lamp according to the measured temperature so as to maintain the surface temperature of the fusing roller within a predetermined range. When the temperature of the fusing roller exceeds the predetermined set value because the thermistor and the controller fail to control the temperature of the fusing roller, a contact of the thermostat opens so as to cut off the supply of power to the halogen lamp.
Such a fusing device using a halogen lamp as a heat source consumes a large amount of electric power. Particularly, when power is turned on, the device requires quite a long warming-up time. The warming-up time may range from several tens of seconds to several minutes. In addition, in such a fusing device, since the fusing roller is heated by radiation emitted from a heat source, heat transmission is slow, and compensation for temperature deviation caused by a decrease in temperature occurring due to contact with a sheet is slow. Thus, it is difficult to maintain the temperature of the fusing roller constant. Moreover, since electric power must be periodically applied to the heat source in order to maintain the temperature of the fusing roller constant in a standby mode in which the operation of the printer is in a pause state, unnecessary electric power is consumed.
To solve the above-described problems, it is an object of the present invention to provide a fusing device which includes a power connecting unit which has improved durability and reliability and which decreases a warming-up time at initial operation or at transition from a standby mode to re-operation in an electrophotographic image forming apparatus.
To achieve the above object of the invention, there is provided a fusing device for an electrophotographic image forming apparatus. The fusing device includes: a heat pipe having a tubular shape and containing a predetermined amount of working fluid, the heat pipe being hermetically sealed at both of its ends; a fusing roller surrounding the heat pipe; a heater installed between the fusing roller and the heat pipe for generating heat; and a power connecting unit for transmitting external electric power to the heater. The heater includes: a resistive coil for generating heat using the electric power transmitted by the power connecting unit, the resistive coil not being covered with a protective coating layer; a first insulation layer provided on the inside of the fusing roller so as to contact the resistive coil; a second insulation layer provided on the outside of the heat pipe so as to contact the resistive coil; and leads for connecting the resistive coil to the power connecting unit at both ends of the heater.
Preferably, each of the first and second insulation layers is formed of at least one mica layer.
Preferably, the power connecting unit includes an electrode inserted into an outer end portion of each of first and second end caps which are installed at both ends of, and on the axis of rotation of, the fusing roller, a brush installed in a through hole formed in a frame supporting the fusing roller so as to contact the electrode, and an elastic unit for making the brush closely contact the electrode for electrical connection.
Preferably, each of the first and second end caps includes a lead hole formed in a lengthwise direction so as to allow each lead to pass therethrough, a bottom portion formed so as to allow the lead passing through the lead hole to be electrically connected to the electrode which is inserted into the corresponding end cap, a first insulation film provided on the bottom portion of each of the first and second end caps so as to isolate the bottom portion from the lead, and a heat sink provided on the first insulation film and electrically connected to the lead.
Preferably, the fusing device further includes a second insulation film formed in the lead hole of each of the first and second end caps for isolating the lead from the lead hole.
Preferably, the fusing device further includes: at least one key formed at a portion of an outer circumference of each end cap, the latter portion engaging an end of the fusing roller; and at least one key way formed at each end of the fusing roller so as to correspond to the key. The key way(s) is (are) formed at the inner side of each end of the fusing roller to be recessed.
Preferably, each of the leads includes a ring electrically connected to the resistive coil at each end of the heater, and a string extending from the ring.